Field of the Invention
The present invention relates to a sheet conveying apparatus and to an image forming apparatus including the same.
Description of the Related Art
In general, an image forming apparatus includes a transfer portion transferring a toner image onto a sheet and a fixing portion having a heating and pressure roller pair disposed downstream in a sheet conveying direction of the transfer portion. The sheet onto which the toner image has been transferred at the transfer portion and fixed by being nipped through the heating and pressure roller pair is then conveyed and discharged out of the apparatus.
The sheet of the type used in the image forming apparatus is normally manufactured by cutting a long and wide base sheet into sheets of predetermined size. There is a case when burr is generated on a cut surface of the sheet cut as described above depending on a cutting method, a cutting device, and cutting history of a cutter. While the burr on the cut surface of the sheet is generated on a sheet edge warping toward a side in which a movable blade is pulled out, a magnitude, a direction and a shape of the burr are different depending on a sheet size and a manufacturing lot and are not always constant.
When a large number of such sheets in which the burr is formed at the sheet edge is conveyed consecutively to the transfer portion or the fixing portion, there is a case when a transfer member such as a transfer roller and a fixing member such as a heating and pressure roller pair are scratched by the burr at the sheet edge. Then, due to the scratch of the heating and pressure roller pair, there is a case when stripes, flaws or unevenness are generated on the image fixed on the sheet. For instance, if a large-size sheet is fixed after consecutively fixing a large number of small-size sheets by the heating and pressure roller pair, there is a case when such stripes, flaws or unevenness are generated on the image fixed on the large-size sheet due to the scratches of the heating and pressure roller pair caused in fixing the small-size sheets. There is a problem that quality of the image on the sheet drops if the heating and pressure roller pair is thus scratched.
As a solution for the scratch of the heating and pressure roller pair caused by the burr, Japanese Patent Application Laid-open No. Hei. 10-218459 for example discloses a technology of correcting the burr by providing a burr correcting portion having a certain irregular shape between a feed roller and a registration roller. That is, according to this technology, the burr correcting portion is composed of a pair of rollers and conveys while pressing a sheet such that a condition of a front edge of the sheet passing through the roller pair is leveled. For example, fine irregularities are formed on surfaces of the roller pair along a sheet feed direction while shifting positions of the irregularities of the roller pair from each other so as to engage and to crush the burr at the front end of the sheet.
Still further, Japanese Patent Application Laid-open No. 2009-198682 discloses a technology of disposing a burr removing portion having a movable removing brush upstream in a sheet conveying direction of a transfer portion and of removing burrs by increasing a rotation speed of the removing brush more than a sheet conveying speed. That is, this technology removes the burrs at side edges of a sheet conveyed through a sheet conveying path by bringing the removing brush disposed on the sheet conveying path upstream in the sheet conveying direction of the transfer portion into contact with the sheet side edges.
Japanese Patent Application Laid-open No. 2013-41210 discloses a technology of disposing a metallic roller pair for crushing burrs of a sheet and of removing the burrs by applying a pressure of about 450 [kgf] in an entire longitudinal direction of the sheet.
However, the burr removing methods described in Japanese Patent Application Laid-open Nos. Hei. 10-218459 and 2009-198682 may possibly cause a large amount of paper powders on the sheet and lower the burr removing functions because the removed paper powders accumulate on a removing portion. It is noted that the ‘paper powders’ include both plant fiber paper powders and powders other than the plant fiber paper powders. Still further, according to the burr removing method described in Japanese Patent Application Laid-open No. 2013-41210, it is necessary to apply an extremely large force on the sheet edge part to crush the burrs, so that a torque of a sheet conveying driving roller may possibly be increased. Meanwhile, while there is an apparatus configured to remove paper powders by blowing air within a sheet conveying apparatus, such configuration may possibly increase a size and a cost of the apparatus.